1. Field of the Invention
The present invention relates to a blood flow velocity calculation apparatus and a method. More specifically, the present invention relates to a blood flow velocity calculation apparatus and a method that can be used for ophthalmologic medical diagnosis.
2. Description of the Related Art
A scanning laser ophthalmoscope (SLO), which is an ophthalmologic apparatus operable based on the principle of confocal laser microscope, is an apparatus that can perform raster scanning on a fundus of an eye (hereinafter referred to a fundus) with a laser beam (i.e., a measuring beam) and can speedily obtain a high-resolution planar image of the fundus based on the intensity of a returned laser beam. Hereinafter, an apparatus capable of capturing a planar image is referred to as an SLO apparatus.
If a measuring beam having an increased beam diameter can be used in the SLO apparatus, the SLO apparatus can acquire a planar image of a retina that is excellent in horizontal resolution. However, when the beam diameter of the measuring beam becomes larger, the acquired planar image of a retina tends to deteriorate in S/N ratio and resolution due to an aberration that may be generated by a subject's eye.
An adaptive optics SLO apparatus is conventionally available to solve the above-described problem. The adaptive optics SLO apparatus includes a wavefront sensor that can perform real-time measurement of the aberration of the subject's eye. The adaptive optics SLO apparatus includes an adaptive optics system equipped with a wavefront correction device that can correct the aberration of the measuring beam or its returned beam that may be generated by the subject's eye. Thus, the adaptive optics SLO apparatus can acquire a planar image having excellent horizontal resolution.
Further, the adaptive optics SLO apparatus is conventionally usable to continuously acquire retinal planar images having excellent horizontal resolution and calculate the blood flow velocity based on a traveled distance of a blood cell in a capillary vessel, as discussed in “Joy A. Martin, Austin Roorda, Direct and Noninvasive Assessment of Parafoveal Capillary Leukocyte Velocity. Ophthalmology, 2005; 112:2219.” The calculation of the blood flow velocity discussed in this literature is performed based on time duration between acquisition of a preceding planar image and acquisition of a succeeding planar image (i.e., a time required to acquire a single planar image).
As described above, the SLO apparatus is an apparatus that includes a scanning unit configured to perform raster scanning on a retina with a measuring beam to acquire each retinal planar image. Therefore, the timing of an image capturing operation is variable depending on the position in an acquired planar image. Therefore, the measuring range for the blood flow velocity to be calculated may depend on the scanning direction of the scanning unit.